Answer:
The periodic trends are patterns that we can find in the periodic table that show specific properties. Those properties nclude metallic character, non metallic character, atomic radius, ionization energy or electronegativity.
If we have to select two we can work with: electronegativity and atomic radius.
Electronegativity:
The electronegativity is a chemical property that describes the ability of an atom to attract electrons. It's useful when determining if a bond between two atoms is covalent or ionic.
Across the periodic table the electronegativity increases from left to right and from bottom to top. We can see the values in the next table and identify that trend.
Elements on the right side of the table almost have their valence shell complete, they can easily gain electrons to become stable. Their electronegativiy is high. On the other hand, the elements on the left side of the period table only have 1 (group 1) or 2 (group 2) valence electrons. It's easier for them to lose electrons, so their electronegativity is low.
Atomic radius:
The atomic radius is one-half the distance between the nuclei of two atoms.
Atomic size decreases from left to right across a a period of elements. In the same period all the electrons are added to the same shell. As the atomic number increases (from left to right) we are adding one proton to the nucleus and one electron to the shell. As the number of protons in the nucleus increases, the nucleus becomes more positivily charged and the nucleus attracts the electrons more strongly. The electrons in the shells are closer to the nucleus, so the size of the atom or the atomic radius decreases.
The atomic size or the atomic radius increases from top to bottom. Down a group the valence electrons occupy higher levels of energy and the valence electrons are further away from the nucleus. As a result the atomic radius is larger as we go down a group.
